1. Field of the Invention
The present invention relates to an anti-backlash nut that causes no backlash between a lead screw and the nut composing a linear reciprocating device used in reciprocating a probe of a measuring apparatus, a table of a precision machine and a die in an extrusion molding machine for example.
2. Description of the Related Art
Hitherto, there has been an anti-backlash nut mechanism of a lead screw as shown in FIG. 9 as an invention illustrated in Japanese Utility Model Publication No. Hei 2-18378 that encompassed elimination of backlash between a lead screw and a nut.
This anti-backlash nut mechanism is designed to eliminate backlash of two nuts 902 and 903 by biasing the two nuts 902 and 903 away from each other by a spring 906 provided between the nuts 902 and 903 which are engaged with (screwed to) a lead screw 901 while engaging a pin 904 with a hole 905 so that the two nuts 902 and 903 turn together in the turning direction.
However, the prior art anti-backlash nut mechanism has had a problem in that either the nut 902, the nut 903 or the spring 906 may be lost because the nut 902, the nut 903 and the spring 906 are separated from each other when the nuts 902 and 903 are unscrewed from the lead screw 901.
U.S. Pat. No. 4,954,032 discloses an anti-backlash nut mechanism in which two nuts and a spring are not separated from each other even when the two nuts are unscrewed from a lead screw. This anti-backlash nut mechanism comprises a female nut segment having a hollow extension, adjustment slots and long guide grooves, a male nut segment having a plurality of guide fingers which are fixed by retaining grooves formed in a body portion and slots formed in a flange, and a compression spring. Both nut segments may be coupled in a body by guiding the guide fingers to the guide grooves and by anchoring lock stops at the edge of the guide fingers in the guide grooves in a condition in which the compression spring is provided in compression between the flanges of the both nut segments.
Accordingly, the anti-backlash nut mechanism has had a complicated structure as described above requiring the complicated female and male nut segments and the plurality of guide fingers formed in a body with the male nut segment. Still more, because the compression spring has been disposed so as to surround the body portion of the both nut segments and the guide fingers after assembly, it has been cumbersome to adjust the engagement of the guide fingers with the adjustment slots and to disassemble the respective parts.